The present invention relates to a method of and a system for unpacking bales such as, for example, pulp bales.
In a paper-making plant having no pulp manufacturing installation, in general, pulp in the form of sheets is carried to the paper-making plant from a pulp-making plant, the pulp in the form of sheets is dissociated by a pulper, and the dissociated pulp is used as raw material.
As shown in FIG. 1, the pulp formed by a stack of pulp sheets is carried and stored in the form of a so-called pulp bale 1. In the pulp bale 1, a pair of first and second packaging sheets 1a and 1b wrap up respectively upper and lower portions of the stack of pulp sheets. A plurality of wire bands 1c extending in vertical planes perpendicular to each other tie the stack of pulp sheets through the first and second packaging sheets 1a and 1b. When it is desired to feed the pulp in the form of the pulp bale 1 into the pulper and to subject the pulp to a dissociation treatment, it is necessary to carry out, by operators' hands, the removal operation of the wire bands 1c from the pulp bale 1 and the removal operation of the packaging sheets 1a and 1b from the stack of sheets.
In recent years, the paper-making plant has become considerably large in scale. In such papermaking plant large in scale, it has been requested to carry out the above-mentioned unpacking operation of the pulp bales 1 automatically without relying upon the operators' hands, in order to efficiently supply a large quantity of pulp raw material. A method of and a system for unpacking pulp bales, which fulfill the above request, have been proposed in Japanese Pat. Application No. 57-9752 said open under No. 58-134844 on Aug. 11, 1983 and the like.
Specifically, as shown in FIG. 2, the unpacking system disclosed in the above-mentioned Japanese patent application comprises a roller conveyer 2 for transporting the pulp bales 1 from below to above as viewed in FIG. 2. A centering device 3 is provided for centering the pulp bales 1 widthwise of the roller conveyer 2. The wire bands 1c are cut by a wire cutting machine 4, and the cut wire bands 1c are drawn and removed out of the pulp bale 1 by a wire removing machine 5. A first vacuum-holding machine 6A is provided for reciprocative movement in a direction intersected with the roller conveyer 2. The first vacuum-holding machine 6A is so arranged as to apply negative pressure to the first packaging sheet 1a to hold the same, and to move the first packaging sheet 1a held under the suction pressure upwardly from the bale 1, thereby removing the first packaging sheet 1a from the bale 1. Then, the bale 1 having removed therefrom the first packaging sheet 1a is turned upside down by an inverting machine 7, which is arranged to surround the roller conveyer 2, such that the second packaging sheet 1b is located at the top of the bale 1 turned upside down. A second vacuum-holding machine 6B is arranged downstream of the inverting machine 7. The second vacuum-holding machine 6B applies negative pressure to the second packaging sheet 1b to hold the same, and to move the second packaging sheet 1b upwardly from the pulp bale 1 thereby removing the second packaging sheet 1b from the pulp bale 1, to expose the stack of pulp sheets. Thus, the unpacking operation of the pulp bale 1 is completed.
By the way, it is necessary to make the wire cutting machine 4 and the wire removing machine 5 correctly grasp the positions of the respective wire bands 1c of the pulp bale 1, in order to cut the wire bands 1c by the wire cutting machine 4 and to draw and remove the cut wire bands 1c out of the pulp bale 1 by the wire removing machine 5.
Conventional, metal detecting means such as a magnetic sensor is employed to detect the position of the wire bands 1c. That is, the metal detecting means is moved horizontally along a confronting side face of the pulp bale 1 to scan the confronting side face. As indicated by the phantom lines in FIG. 2, however, if the confronting side face of the pulp bale 1 is inclined with respect to the direction in which the metal detecting means moves to scan the confronting side face of the pulp bale 1, the metal detecting means might be caught by the confronting side face of the pulp bale 1. This makes it difficult that the metal detecting means moves to scan the confronting side face of the pulp bale 1.
Further, as described previously, the packaging sheets 1a and 1b are removed from the pulp bale 1 by the vacuum-holding machines 6A and 6B. Each of the vacuum-holding machines 6A and 6B comprises a vacuum-holding head which is provided with a plurality of suction pads. When the negative pressure is applied to the packaging sheets, for example, to the first packaging sheet 1a through the suction pads, air is drawn from spaces between the first packaging sheet 1a and the top pulp sheet of the stack and between each pair of adjacent pulp sheets at the top of the stack, to bring the spaces to negative pressure. This causes the first packaging sheet 1a to be brought into close contact with the several upper pulp sheets of the stack, making it difficult to separate the first packaging sheet 1a from the stack of sheets. By this reason, as the first packaging sheet 1a is moved upwardly by the vacuum-holding head, the several upper pulp sheets are held under vacuum against the first packaging sheet 1a and are removed together with the first packaging sheet 1a out of the stack of sheets. Alternatively, the several pulp sheets held under vacuum against the first packaging sheet 1a fall down onto the stack of sheets during upward movement of the first packaging sheet 1a, causing the stack of sheets to get out of shape. This is an obstacle to transfer of the stack of sheets to the subsequent processing step.
Moreover, the pulp bale 1 has, on or in its surface, a large number of damages due to various shocks during transportation, and a large number of recesses or indentations due to tying-up of the pulp bale 1 by the wire bands 1c. Because of such damages and recesses, the suction pads of the vacuum-holding machines 6A and 6B cannot be brought into sealing contact with the packaging sheets 1a and 1b. This makes it impossible to apply sufficient negative pressure to the packaging sheets 1a and 1b through the suction pads. Thus, there is an anxiety that the packaging sheets 1a and 1b are not vacuum-attracted to the suction pads.